We have, [A]x×x+5 [where x = number at rows and x+5 = number of column] and [B]y×(11−y) where y = number of rows and 11−y = number of columns] According to the matrix rule AB exist if ⇒Number of column of A = number of raw of B ⇒x+5=y...(i) and BA exist if ⇒ Number of column of B = Number of raw of A ⇒11−y=x...(ii) By solving Eq. (i) and Eq. (ii), we get x=3 and y=8